Circuit arrangements of this generic type are known in principle, and are frequently used in converters of any type, specifically inverters, in order to permit the operation of the converter or inverter for its intended purpose. To this end, it is in fact necessary to identify current characteristics, specifically for output currents of the converter or inverter. A key parameter is the identification of a zero-current in the output current of the converter or inverter.
Inverters of this generic type and methods for the operation thereof are also known in principle, for example from DE 10 2008 027 126 A1. Inverters are a form of energy converter, by means of which a d.c. voltage can be converted into an alternating voltage, specifically a single-phase or a three-phase alternating voltage. Inverters are now used in the form of “static” energy converters, meaning that, unlike dynamic energy converters, they feature no mechanical moving components, specifically rotating components, for the purposes of energy conversion. Inverters of this generic type in the form of static energy converters are generally configured as switched-mode electronic energy converters and, to this end, are provided with at least one half-bridge module, by means of which a d.c. voltage delivered to an intermediate circuit capacitor on an intermediate circuit may be converted into an alternating electric voltage. To this end, the half-bridge module is provided with two series-connected semiconductor switches, which can operate in cyclic mode by means of a clock-pulse generator such that, in the required manner, the alternating voltage is delivered on a center terminal of the half-bridge module, which is constituted by an electrical interconnection point of the two semiconductor switches in the half-bridge module. A circuit topology of this type is also described as a half-bridge circuit. Accordingly, an inverter of this type is designed for “single-phase” operation.
A high-capacity variant of an inverter of this type is provided with two parallel-connected half-bridge modules, whereby the magnitude of the alternating voltage generated is essentially doubled. To this end, the half-bridge modules are controlled in a correspondingly complementary arrangement. A circuit topology of this type is also described as a full-bridge circuit.
Inverters are also used, specifically for the constitution of a three-phase alternating voltage system, wherein at least one half-bridge module is provided for each of the alternating voltage phases. A circuit topology of this type is also described as a half-bridge circuit. Naturally, the inverter may also be provided with a pair of half-bridge modules for each phase, such that the circuit topology of a full-bridge circuit is constituted for each phase.
Inverters of this generic type are frequently used in charging stations, which are used for the wireless power coupling of an electrically-powered vehicle, for the purposes of the charging of an electric energy storage device in said electrically-powered vehicle. A wireless power coupling is formed, which obviates the need for a complex mechanical connection by means of a cable. To this end, on both the charging station side and the vehicle side, coil arrangements are generally provided respectively which, during the charging process, are positioned opposite each other, and permit the formation of a power coupling by the use of an alternating magnetic field. An arrangement of this type is known, for example, from KR 10 2012 0 016 521 A.
In order to be able to generate an appropriate alternating magnetic field in the charging station, the latter, in addition to an appropriate coil for this purpose, is also provided with an inverter which is connected to the coil and which supplies a corresponding alternating current to the coil. For the reliable operation of the charging station, and specifically of the inverter, it is necessary to identify the zero-currents. To this end, DE 10 2008 027 126 A1, for example, discloses a current sensor which is connected to a circuit arrangement which permits the evaluation of current via a differentiating circuit element. The circuit disclosed therein detects the falling current ramp by means of a differentiator, and compares the latter with a tripping signal for a semiconductor switch in a half-bridge module of the inverter. In order to permit the reliable operation of this circuit, a sinusoidal current characteristic is required which, insofar as possible, is free of harmonics. Specifically, there must be no superimposed interference. In practical operation, this results in problems, in that zero-currents cannot be detected with sufficient accuracy, thereby resulting in the inadequate control of the inverter.